Summary

On 23 December 2009, a Garlick Helicopters Incorporated TH-1F helicopter, registered VH-UHD, was engaged in aerial firefighting operations in the Nangar National Park, New South Wales. At about 200 ft above ground level, the nose of the helicopter unexpectedly yawed to the right. The pilot made a corrective input on the tailrotor pedals, but was unable to stop the yaw and the helicopter began to rotate. The pilot guided the helicopter to a less-timbered area for an emergency landing. The helicopter descended into the trees and was seriously damaged. The pilot, the sole occupant, was seriously injured.

The loss of directional control was due to a structural failure in the helicopter's tailrotor control system, likely precipitated by the failure of an attachment bolt.

The investigation identified a safety issue with the maintenance and operation of ex-military helicopters being used in repetitive heavy lift operations. In response, on 5 July 2011, the Civil Aviation Safety Authority published Airworthiness Bulletin 02‑40 Issue 1 to advise operators and maintainers to investigate the basis for, and the correct implementation of, the continuing airworthiness requirements of the applicable type certificate data sheet and incorporated supplemental type certificates, particularly in regard to the retirement lives of all life-limited components.

Safety Issue

The scheduled maintenance requirements for ex-military UH-1 series helicopters may not adequately address the increased risk of fatigue failures associated with repetitive heavy lifting operations that were not considered in the original design fatigue calculations.

Safety issue details

Issue number:

AO-2009-081-SI-01

Who it affects:

All operators and maintainers of ex-military helicopters engaged in repetitive lift missions